For the benefit of clarity the present invention will be described in relation to bus networks. However, the reader will appreciate that the present invention is equally applicable to other network systems such as, for example, daisy chain systems.
A bus network is a plurality of conductors, which serve as a common connection for a group of devices. Although transmission bus networks may comprise any number of conductors, for simplicity the present invention will be described in relation to a two-conductor bus network. However, the reader will appreciate that the invention is equally applicable to networks having more than two conductors.
In order to substantially mitigate, or limit, errors in signals being transmitted, maintenance of the integrity of the transmitted signal and minimising propagation delays and power consumption are important considerations in the engineering of transmission bus networks.
These considerations are substantially addressed by terminating the network with a terminating circuit having appropriate matching impedance. It is normal practice to terminate the network at both ends, that is, at the host and at the last node. This is generally carried out by manual selection and installation of the termination circuit, which typically comprises a terminating resistor in series with a terminating capacitor. A typical network will have multi-drop connections at nodes, which are interfaced to local devices.
A disadvantage of known networks of this type is that, upon occurrence of a fault in the network system such as, for example, an open circuit, the signal integrity is lost. Furthermore, such faults are usually difficult to locate within a network and, in such a state, the network is difficult to maintain in a stable condition. This results in considerable amounts of time being spent locating and fixing the fault and maintaining communication between the host and the nodes in the network until the fault is fixed, which is undesirable.
Also, the signal integrity is dependent on the engineer ensuring terminating circuits are specified and fitted correctly and that none of the nodes upstream of the end node are fitted with terminating circuits. Furthermore, if a change or modification is carried out to the network it is necessary for the engineer to check the impedance characteristics of the whole network system. Again, this is undesirably time consuming and expensive.